A displacement device is a device which bears the fifth wheel coupling of a tractor vehicle, allowing the fifth wheel coupling to be displaced in the longitudinal direction of the vehicle, wherewith means are provided whereby the fifth wheel coupling can be fixed in various positions. Such a displacement device is disclosed in, e.g. DE AS 1780488.
In general, a tractor vehicle which has a fifth wheel coupling has a frame structure comprised of two interiorly open C-profiles which are joined to crossbeams. Often, the C-profiles are provided with auxiliary frame means for mounting the displacement device. A displacement device disclosed in DE 19944684 C1 has a base frame having a generally flat construction which base frame is connected to the auxiliary frame means by screw means or by welding. The base frame is comprised of at least two mutually parallel base bars each of which bears a toothed bar on which the upper part or upper carriage with the fifth wheel coupling and the bearing blocks which support the fifth wheel coupling is displaceably guided. In order to fix the upper part or upper carriage to the base bars, locking pieces are provided on the bearing blocks, which locking pieces can be brought into form-interlocking engagement with the toothed bar.
In order to displace the upper part, it is necessary to temporarily remove the locking pieces from the engagement zone of the toothed bar; this allows the upper part to be moved in the forward or rear direction on the base bars.
A major drawback of the known displacement devices is that the base bars are costly to fabricate, because of the necessity to weld the toothed bar to the profile or toothed profile. Also the displacement device is heavy because of the toothing over the entire length of the toothed bar, even though only 2-3 teeth are in engagement at a given time.